The present invention is broadly concerned with cannula devices, and more particularly relates to cannula assemblies for use in arthroscopy or similar medical or surgical procedures wherein the sensing of pressure in the body joint or at the site of the procedure is a factor.
U.S. Pat. Nos. 4,650,462 and 4,820,265, are directed to equipment for use in arthroscopic procedures, which procedures are generally described in the patents. Such procedures have resulted in the development of number of special purpose cannulas for inflow and outflow of fluid, as well as for pressure sensing in the joint, including:
1. A dedicated pressure sensing cannula which is inserted into the joint in the manner of a large hypodermic needle, and connected to a pressure sensing line, as for example, noted in the tube set of U.S. Pat. No. 4,820,265. PA1 2. A dedicated outflow cannula comprising a tube between 3 mm and 6 mm in diameter which is inserted in the joint and connected to the outflow line. PA1 3. A combination inflow cannula consisting of concentric tubes with the inner tube approximately 3 mm and the outer tube approximately 4 mm in diameter. A small annulus is defined between the tubes which is used to sense the fluid pressure in the joint. The larger inside diameter of the inner tube carries the inflow from the input tube of the pump. PA1 4. A combination outflow cannula which is similar to the combination inflow cannula except that the inner tube carries the outflow from the joint while the annulus senses the pressure. PA1 1. Inflow through the arthroscope cannula, pressure sensing by a dedicated pressure sensing cannula, and outflow by a dedicated outflow cannula. PA1 2. Inflow and pressure sensing through a combination inflow cannula, and outflow through the arthroscope cannula. PA1 3. Inflow through the arthroscope cannula, and outflow and pressure sensing through a combination outflow cannula.
In an arthroscopic procedure, there is always at least one additional cannula involved, the arthroscope cannula in which the scope or viewing instrument is positioned. This cannula will normally incorporate means for fluid communication with the joint provided by the space defined between the outside diameter of the inserted arthroscope and the inside diameter of the arthroscope cannula tube.
From the above, it will be recognized that the doctor has many choices for setting up the joint for the arthroscopic procedure. Some of the most common are:
Methods 2 and 3 above are the ones most favored by doctors since only two incisions are required, as opposed to three incisions for method 1. A desirable alternative to methods 2 and 3, recognized in the development of the present invention, would be the incorporation of pressure sensing in an arthroscope cannula. Only two portals or incisions would be required, with inflow and pressure sensing in the arthroscope cannula, and outflow using a dedicated outflow cannula. This has a big safety advantage since both pressure sensing and inflow occur together. The same safety advantage is present in method 2 above, however, suction may be required to assist outflow.
An initial proposal was to use concentric tubes with an annular passage provided therebetween in the manner of the combination inflow and outflow cannulas. As far as the fluid control system was concerned, the cannula was acceptable. However, because of its manner of construction, with the spaced concentric tubes, a little over 1 millimeter was added to the diameter of the arthroscope cannula. This was considered undesirable and unacceptable to the doctors/users of the device. Thus the problem still remained as to how to provide for acceptable pressure sensing utilizing the arthroscope cannula.